Plain English Meaning
It is the track record of how a piece of special airspace has been used over time. Looking at past activity helps controllers and pilots predict whether it is likely to be busy or quiet right now.
Full Definition
A pattern of recurring activity within a special use airspace (SUA) — such as a Military Operations Area, Restricted Area, or Warning Area — established by reviewing how often, at what times, and at what altitudes the airspace has actually been used in the past. Air traffic controllers and pilots use this historical record to judge whether the airspace is likely to be active or available for transit when current status information is not available.